Acrylic copolymers as additives for inhibiting paraffin deposition in crude oils, and compositions containing same

ABSTRACT

Acrylic copolymers for use as additives for inhibiting paraffin deposition in crude oils, and compositions containing the oils and said additives, are disclosed. Specifically, polymeric additives useful for inhibiting paraffin deposition in and improving the flow properties of crude oils, and compositions containing the crude petroleum oils and said additives, are disclosed. Said additives are essentially alcohol acrylate copolymers comprising 10-50 carbons with special chain distributions, as well as the corresponding 2- and/or 4-vinylpyridine terpolymers.

FIELD OF THE INVENTION

The area of the invention described here is that of crude petroleum oilsand additives to improve the production conditions.

Crude oils may contain large fractions of paraffins, the exact quantityand nature of which are variable, depending on the producing field. Atthe temperature of the wells, the paraffins are liquid and dissolve inthe crude oil. As the oil rises to the surface, its temperature becomeslower and the paraffins in it crystallize, forming a three-dimensionalnetwork of needles and flakes. This results in loss of fluidity whichmakes production, transportation, storage and even the treatment ofthese oils very difficult. Plugging of the pipelines and treatmentapparatuses occurs frequently.

BACKGROUND OF THE INVENTION

Numerous methods have been proposed to solve this problem, such asmechanical scraping or heating of the walls. These methods are costlyand cannot always be applied.

In order to improve the rheology of crude petroleum oils, SHELL did thepioneering work with FR 1,575,984: it teaches that macromolecularcompounds of the “comb” type, constructed on the model of a principalhydrocarbon chain on which fairly long lateral hydrocarbon chains aregrafted, that is, chains with at least 14 carbon atoms and at most 30carbon atoms, can perturb the crystallization of heavy paraffins. Thisproperty is manifested well by macromolecules, which have an averagemolecular weight (number-average molecular weight M_(n), the definitionof which is recalled here:

M_(n)=Σ_(i)NiMi/Σ_(i)Ni,

where Mi are the molecular weights of the individual species Ni presentin the polymer) is between 1000 and 1,000,000 and preferably between4000 and 100,000. Thus, the utilization of additives was suggested, mostfrequently polymeric additives, the role of which is to retard or tomodify the crystallization of paraffins and thus improve the flowproperties of the oil and prevent agglomeration of the crystals formedon the walls.

Numerous studies then attempted to improve the efficacy of these firstadditives of polymeric nature, either by the synthesis or by theformulation, in order to adapt them to different types of crude oilsencountered and to ameliorate successively the difficulties of synthesisand/or handling of the various generations of products, for example,among the most effective ones, C₁₈₋₃₀ acrylate copolymers, preferablymainly C₂₀₋₂₂ ones, with a heterocyclic monomer, notably vinylpyridine[U.S. Pat. Nos. 2,839,512 (1958) and FR 2,128,589 (1972) of SHELL]. Thepresence of polar units confers a dispersing character to the polymer,which permits avoidance of deposition of paraffins on the wall. Now,because of the higher reactivity of long-chain acrylates in comparisonto the polar comonomers, incorporation of the latter is generally verydifficult and the dispersing effect related to the rate of incorporationof the polar comonomer frequently remains very low.

In spite of these successive improvements, these additives cannot beapplied universally to all crude oils, each one representing aparticular case and presenting its own problems.

DESCRIPTION OF THE INVENTION

It was now found very unexpectedly that the performance of the paraffininhibitors of the alkyl acrylate copolymer type or alkylacrylate/vinylpyridine type can be improved considerably when a part ofthe monomer alkyl acrylate units participating in the polymer chains,represented by

in which R is H or CH₃,

in which Ri remainder are linear saturated Ri-OH alcohol groups, thenumber of carbon atoms of which range from approximately 10 toapproximately 50, and come from an acrylic cut having a specialdistribution of the alkyl chains, called distribution “U” for thepurposes of the present patent. Distribution “U” is defined as thedistribution of alkyl chains as a function of the length of the chains,here always with even number of carbon atoms, the envelope of which isvery regular, the weight-average molecular weight M_(w) being between375 and 700, and the number-average molecular weight Mn being between375 and 840, as well as their poly-dispersity factor M_(w)/M_(n) between1.0 and 1.2 (M_(w) is the weight-average molecular weight, the formulafor calculating it being recalled here:

M_(w)=Σ_(i)NiMi²/Σ_(i)NiMi,

where Mi are the molecular weights of individual species Ni present inthe polymer). FIG. 1 gives a representation of the distribution of thealcohols distributed according to a “U”-type distribution law with amean molecular weight of 425 (in order to obtain such alcohols, see U.S.Pat. No. 4,426,329). The polymeric acrylates obtained by a singlepolymerization of monomers with a “U” distribution cannot bedistinguished particularly from those that one obtains from arbitrarymonomers, including here products usually available to the expert in thefield and in which no particular distribution of the length of theattached chains is expected, in other words, the distribution of whichis any distribution, but, in any case, it is not a “U” distribution.What is very astonishing and from which the Applicant derives all theadvantageous consequences, is that a powerful synergism develops withregard to the inhibition of crystallization of paraffins in petroleumoils when the products of the “U” class and “non-U” class aredistributed within the same polyacrylate or polyacrylate/vinylpyridinecopolymer. As with all synergism in mixtures which can be highlyvariable in composition, the rules are very delicate to discern, but theguiding principles can be formulated, which will be most useful to theperson in the field: The “U” components are centered on average lengthsof the hanging chains i_(u) in the copolymer which are longer than thatof the i_(nu) of the “non-U” component, and the weight of the totalnumber of units with “U” chains in the copolymer is relatively low incomparison to the total number of “non-U” units. According to theinvention, the term vinylpyridine includes 2-vinylpyridine,4-vinylpyridine or the mixture of the two. The copolymers of theinvention contain 1 to 10% of these.

In terms of structural description, one can say that alkyl acrylatecopolymers or alkyl acrylate/vinylpyridine copolymers with aweight-average molecular weight between 5000 and 500,000, preferablybetween 40,000 and 350,000 form part of the invention, and that inthese, with acrylate monomer units which participate in the polymerchain

in which R is H or CH₃,

in which Ri are remainder saturated linear Ri-OH aliphatic alcoholswhere i represents the number of carbon atoms of these groups, extendingbetween 10 and 50 carbon atoms, and following a distribution law whichis the superposition of a “U” distribution law in which the i values areeven numbers within the upper range of the interval of 24-50, the centervalue of which is i_(u), and a “non-U” distribution law in which the ivalues are odd or even, lying in the lower range of 10-22 of theinterval and the centered value of which, i_(nu), is such thati_(nu)<i_(u), the weight ratio of all the units

with Ri distributed according to the “U” law to the total number ofunits distributed according to the “non-U” law, ranges from 1:99 to50:50, and preferably from 5:95 to 50:50.

The paraffin inhibitor formulations incorporating these copolymers asessential components eliminate the disadvantages cited above and permitthe realization of a series of additives with a broad spectrum ofutilization, having good solubility in crude oils, which have an effectboth on the crystallization of paraffins as well as on the dispersion ofcrystals already formed. They retard the crystallization of paraffins,the distribution of which generally lies between C60 and C70, permittinglowering of the flow point and the viscosity of these oils andfacilitating their transportation, storage and treatment. They areincorporated easily in crude oils of greatly diverse origins.

METHOD OF CARRYING OUT THE INVENTION

The copolymers according to the invention can be obtained according to asimple and not very restricted polymerization process. Thus, theinvention offers to the expert in the field the possibility of selectingthe cut of polymeric alcohols which will have the best similarity to thecrude oil to be treated and which will correspond to the best efficacy,using simple routine tests. Results in this direction are presented inthe examples.

The best results are obtained with statistical “U” and “non-U” alcoholacrylates, statistical copolymers or “U” and “non-U” alcohol acrylatesand vinylpyridines which contain 5 to 50% of “U” monomers centered atC₂₄ to C₅₀, the characteristics and the efficacy of the copolymers beingdefined by the choice of the solvent/initiator pair. The preferred “U”comonomers are alcohol acrylates centered between C₃₀ and C₄₀.

The polymeric additive according to the invention is obtained either bypolymerization of acrylate monomers in toluene, xylene, and, generallyspeaking, in any aliphatic or aromatic solvent with a boiling pointbelow 300° C., which is chemically inert toward the monomers, in whichboth the monomers as well as the copolymer are soluble, or in the caseof copolymers containing only acrylates, by mixing acrylate homopolymersobtained separately in the same solvent. The polymerization temperaturemay vary fairly widely as a function of the radical initiator used, forexample, between 50° and 150° C. and preferably between 70° and 120° C.The pressure may vary between atmospheric pressure and pressures lowerthan or equal to 30 bars.

The presence of 1 to 10% of 2-vinylpyridine and/or 4-vinylpyridine unitsin the copolymer chains according to the invention improves the efficacysignificantly, at least toward certain types of oils. An example of thisis reported later.

The catalysts are generally chosen from compounds that generate freeradicals that are soluble in the reaction medium, for example,peroxides, such as benzoyl, acetyl, ditertiary-butyl peroxide,tertiarybutyl perbenzoate, tertiarybutyl peroctoate or azo compounds,such as azobisisobutyronitrile. Generally, 10⁻⁵ to 10⁻¹ mole of catalystand preferably 5·10⁻⁴ to 10⁻² mole per mole of monomer is used.

The global concentration of monomer in the solvent may range from 10 to90% by weight, the preferred concentrations ranging from 20 to 70% inorder to control the molecular weight and the pumpability of solutionscontaining the polymeric additives. The degree of polymerization ismeasured by gel-permeation chromatography (GPC) which permits one toobtain the weight-average and number-average molecular weights inequivalents of polystyrene, as well as the polydispersity index Pd ofthe polymer.

The weight-average molecular weight M_(w) and number-average molecularweight M_(n) of the vinyl copolymer used alone or in combination with asecond copolymer according to the invention may vary within wide limitsdepending on the nature of the crude to be treated, that is, between5000 and 500,000 for the M_(w), preferably 40,000 to 350,000, and thepolydispersity Pd can vary between 1.5 and 7.5.

INDUSTRIAL APPLICATION

The copolymers according to the invention are used in the crude oils atdoses that can vary within wide limits, depending on the nature,structure and the molecular weight of the copolymer to be used, on thenature of the quantity of the paraffin waxes present in the crude oiland on the desired performance in lowering the flow point; they may varyfrom 5 to 5000 ppm by weight, preferably from 10 to 2000 ppm. They havea favorable influence on the rheology of the crude oils, in particular,on their viscosity characteristics as a function of the temperature andof the shearing rate which controls in particular the pressure necessaryat restarting of an installation (pipeline, wells) that was stoppedbefore, by varying their flow point or temperature of solidification,their initial crystallization point, their flow by simple gravity, andthe deposits that are formed at the contact with cold walls. All thesecharacteristics are highly important for the production, transportationand storage of oils and some of these will be illustrated in laboratorytests aimed at evaluating the efficacy of these additives.

The antiparaffin compositions according to the invention are constitutedof solutions of these copolymers or additives at concentrations rangingfrom 2 to 90% by weight, preferably from 20 to 70% by weight in solventswhich are soluble in the crude petroleum oils to be treated and whichmay be advantageously the solvents used during the polymerization.

EXAMPLES

The method of obtaining the various homopolymer, copolymer or terpolymercompositions are described below, serving as examples orcounterexamples; the characteristics of the copolymers obtained whichare summarized later in Table I are also described.

In these examples, the monomeric “non-U” acrylates 18-22 are acrylatesof alcohols with approximately 18-22 carbon atoms (marketed byElf-Atochem S.A. under the name of Norsocryl® 18-22), the composition ofwhich, expressed in weight %, is the following:

0<C₁₂-C₁₆<10%

0<C₁₆-C₁₈<40%

50<C₂₀-C₂₂<100%

0<C₂₄-C₃₀<10%

“U”425 is a cut of monomeric alcohol acrylates obeying the law of “U”distribution, centered at 28-30 carbon atoms, with an average molecularweight of 425. “U”550 thus designates a cut of alcohol monomer acrylate,obeying the “U” distribution law, centered at C₄₀, where the meanmolecular weight is 550. The term m.18 designates a reputedly purestearyl methacrylate.

The alcohol acrylates are obtained by methods well-known to the expertin the field, by direct esterification or transesterification catalyzedby zirconium acetylacetonate.

In Table I, the columns M_(n), M_(w) and Pd stand, respectively, for thenumber-average molecular weight, weight-average molecular weight and thedispersion coefficient, which is the ratio of M_(w) to M_(n).

EXAMPLE I “Non-U” Acrylate Homopolymer C₁₈-C₂₂ (M_(w)˜56,000)

Into a 1 m³ reactor, 438 kg of n-alkyl acrylate with a mean chain lengthof C₁₈ to C₂₂ in 359 kg of SOLVANTAR 340® (which is a reaction mediumwith approximately 55% dry extract), is introduced. The temperature ofthe reactor is brought gradually to 40° C. under vacuum with bubbling ofnitrogen and it was maintained there for 30 minutes and then at 100° C.keeping the nitrogen bubbling on. Then, over a period of 1 hour 30minutes, 3 kg of tert-butyl perbenzoate (LUPEROX.P® or TRIGONOX.C®) isadded continuously between 100° and 105° C., while following theviscosity of the reaction medium. This was found to be stable 2 to 3hours after the introduction of the initiator. The total polymerizationtime is 6 hours for a polymerization yield greater than 98%. The productis then brought to 37% active material by the addition of SOLVANTAR340®.

EXAMPLE Ia Homopolymer of C₁₈-C₂₂ Acrylate (M_(w)˜119,000)

The same operating conditions are used as described in composition I, byreplacing the SOLVANTAR 340® by xylene.

EXAMPLE II Homopolymer of C₁₈-C₂₂ Acrylate (M_(w)˜104,000)

Into a 1 m³ reactor, 438 kg of n-alkylke [sic] acrylate with a meanchain length from C₁₈ to C₂₂ in 359 kg of SOLVANTAR 340® is introduced.The temperature of the reactor is brought gradually to 40° C. undervacuum while bubbling nitrogen and was maintained there for 30 minutes,and then at 80° C., while bubbling nitrogen. Over a period of 1 hour and30 minutes, 8 kg of dibenzoyl peroxide (LUCIDOL CH 50®) is addedcontinuously between 80° and 85° C. while following the viscosity of themedium. The viscosity becomes stable 1 hour after the end ofintroduction of the initiator. The total polymerization time is 4 hoursfor a polymerization yield greater than 98%. The product is then broughtto 37% raw material by the addition of SOLVANTAR 340®.

EXAMPLE III Homopolymer of C₁₈-C₂₂ Acrylate (M_(w)˜128,000)

Into a 1 m³ reactor, 558 kg of n-alkylke [sic] acrylate with a meanchain length of C₁₈-C₂₂ in 239 kg of SOLVANTAR 340® is introduced(reaction medium at 70% dry extract). The temperature of the reactor isbrought gradually to 40° C. under vacuum while bubbling nitrogen and wasmaintained there for 30 minutes, and then at 100° C. while maintainingthe bubbling of nitrogen. Then, over a period of 1 hour 30 minutes, 3 kgof tert-butyl perbenzoate (LUPEROX.P® or TRIGONOX.C®) is addedcontinuously between 100° and 105° C., following the viscosity of themedium, which becomes stable 2 to 3 hours after the end of introductionof the initiator. The total polymerization time is 6 hours for apolymerization yield greater than 97%. The product is then brought to37% active material by the addition of the solvent SOLVANTAR 340®.

EXAMPLE IV Homopolymer of C₁₈-C₂₂ Acrylate (M_(w)˜268,000)

Into a 1 m³ reactor, 518 kg of n-alkylke [sic] acrylate with a meanchain length between C₁₈ to C₂₂ in 222 kg of xylene is introduced(reaction medium with 70% dry extract). The temperature of the reactionis brought to 40° C. under vacuum while bubbling nitrogen through it andwas maintained at this temperature for 30 minutes, then at 100° C.,continuing the bubbling of nitrogen. Then, over a period of 1 hour and30 minutes, 3 kg of tert-butyl perbenzoate (LUPEROX.P® or TRIGONOX.C®)is added continuously between 100° and 105° C., while following theviscosity of the reaction medium. This becomes stable 2 to 3 hours afterthe end of introduction of the initiator. The total polymerization timeis 6 hours for a polymerization yield greater than 97%. The product isthen brought to 37% active material by the addition of xylene.

EXAMPLE V Copolymer of C₁₈-C₂₂ Acrylate and of Acrylate of the “U”-typeCentered at C₂₈₋₃₀—In the Table “U”425 (Ratio 90/10—M_(w)˜123,000)

The reaction was carried out in xylene (dry extract—65%).

EXAMPLE VI Copolymer of C₁₈-C₂₂ Acrylate and “U”425 Acrylate (Ratio80/20—M_(w)˜134,000)

The reaction was carried out in xylene (dry extract—65%).

EXAMPLE VIa Copolymer of C₁₈-C₂₂ Acrylate and “U”425 Acrylate (Ratio80/20—M_(w)˜64,000)

The reaction was carried out in xylene (dry extract—55%).

EXAMPLE VII Copolymer of C₁₈-C₂₂ “non-U” Acrylate and “U”425 Acrylate(Ratio 70/30—M_(w)˜146,000)

Into a 1 m³ reactor, 363 kg of n-alkyl acrylate with a mean chain lengthof C₁₈ to C₂₂ and 155 kg of “U”425 acrylate (ratio 70/30) in 279 kg ofxylene (dry extract—65%) was introduced. The temperature of the reactorwas gradually brought to 40° C. under vacuum while bubbling nitrogen,maintaining it at this temperature for 30 minutes, then it was broughtto 100° C. with the bubbling of nitrogen continued. Then, over a periodof 1 hour 30 minutes, 3 kg of tert-butyl perbenzoate (LUPEROX.P® orTRIGONOX.C®) was added between 100° and 105° C. while following theviscosity of the medium. This was found to become stable 2 to 3 hoursafter the end of the introduction of the initiator. The totalpolymerization time was 6 hours for a polymerization yield greater than97%. The product was then brought to 37% active material by the additionof xylene.

EXAMPLE VIII Copolymer of C₁₈-C₂₂ Acrylate and “U”425 Acrylate (Ratio50/50—M_(w) Cannot Be Measured) EXAMPLE IX Homopolymer of “U”425Acrylate (M_(w) Cannot Be Measured)

The same operating conditions as those described for composition III areused. The total polymerization time is 6 hours for a polymerizationyield greater than 95%. The product is then brought to 37% activematerial by the addition of xylene.

EXAMPLE X Copolymer of C₁₈-C₂₂ Acrylate and of a “U”550 Acrylate withthe Alcohol “U” centered at C₄₀ (Ratio 90/10—M_(w)˜162,000)

The reaction was carried out in xylene (dry extract 65%).

EXAMPLE XI Copolymer of C₁₈-C₂₂ Acrylate and “U”550 Acrylate (Ratio95/5—M_(w)˜150,000)

The reaction was carried out in xylene (dry extract 65%).

EXAMPLE XII Copolymer of Stearyl Methacrylate and “U”425 Acrylate (Ratio70/30—M_(w)˜317,000) EXAMPLE XIII Terpolymer of Stearyl Methacrylate,C₁₈-C₂₂ Acrylate and “U”425 Acrylate (Ratios 14/56/30—M_(w)˜180,000)EXAMPLE XIV Terpolymer of Stearyl Methacrylate, C₁₈-C₂₂ Acrylate and“U”425 Acrylate (Ratios 28/42/30—M_(w)˜214,000) EXAMPLE XV Terpolymer of4-vinylpyridine, C₁₈-C₂₂ Acrylate, and “U”425 Acrylate (Ratios5/66.5/28. 5—M_(w)˜221,000) EXAMPLE XVI (Counter-example) Copolymer of4-Vinylpyridine and C₁₈-C₂₂ Acrylate (Ratios 5/95—Solubility Failure,M_(w) Not Measurable) EXAMPLE XVII (Counter-example) Copolymer of4-Vinylpyridine and “U”425 Acrylate (Ratios 5/95—Solubility Failure,M_(w) Not Measurable) EXAMPLES XVIII TO XXII

In these examples, various compositions with 37% additive wereincorporated into crude oils—that is, at 20° C. above the flow point ofthe crude under agitation—at concentrations ranging from 100 to 1500ppm. The performances obtained for the polymers according to theinvention were compared with that of the control with Shell Swimm 5X®and Shell Swimm 11T®, two well-known paraffin inhibitors marketed by theSHELL OIL COMPANY.

TABLE I composition “non-U” homopolymer M_(n) M_(w) Pd 18-22 I 22,70056,000 2.5 100 Ia 41,600 119,000 2.9 100 II 41,400 104,000 2.5 100 III32,500 128,000 4.0 100 IV 39,100 268,000 6.9 100 copolymer “non-U” 18-22/“U”425 V 38,700 123,00 3.2 90/10 VI 39,200 134,00 3.4 80/20 VIa28,100 64,300 2.3 80/20 VII 36,500 146,000 4.0 70/30 VIII not not not50/50 homopolymer measurable measurable measurable “U”425 IX not not not100 copolymer measurable measurable measurable “non-U” 18- 22/“U”550 X34,000 162,000 4.8 90/10 XI 42,000 150,000 3.6 95/5 copolymer m.18/“U”425 XII 190,000 317,000 1.7 70/30 terpolymer m.18/“non- U” 18- 22/“U”425XIII 67,000 180,000 2.7 14/56/30 XIV 98,000 214,000 2.2 28/42/30copolymer VP 4-VP/“non- U” 18- 22/“U”425 XV 440,000 221,000 5.05/66.5/28.5 XVI not not not 95/0/5 measurable measurable measurable XVIInot not not 0/95/5 measurable measurable measurable

In order to determine the efficacy of these polymers as inhibitors ofthe deposition of paraffins, there are several approaches, which includethe rheological behavior of the crude and lowering of their flow point.

By modifying the phenomena of crystallization of crude oils, theparaffin inhibitors influence their rheological characteristicsdirectly. It is clear that, during the industrial utilization of theseproducts during production/transport, the rheological measurements willgive a direct account of their performance.

In particular, the viscosity is measured as a function of the shearrate.

Crude oils generally have a rheological behavior of the Binghamianplastic fluid type, that is, the shearing stress varies linearly withthe shearing rate. In contrast to Newtonian fluids, it is necessary toapply a minimum force in order to put the fluid into movement. Thisforce corresponds to the minimum shear stress (yield value or yieldpoint). This measure is currently practiced on production sites becauseit permits evaluation with a simple calculation of the pressure which isnecessary to start up again an installation (pipe, wells) that wasstopped before. It is this start-up pressure that the paraffin inhibitoradditives are capable of reducing considerably, by disorganizing thecrystalline network being formed.

In order to measure this yield value, a FANN type viscosimeter is usedand the stress is measured as a function of the speed gradient appliedto the mobile part. The curve obtained is an asymptotic curve, and it issufficient to extrapolate the right asymptote to zero shear stress toobtain the value of the flow threshold:

ΔP=4Lτ/D

The flow point or flow temperature of the crudes is also a veryimportant characteristic in evaluating the rheological properties of acrude oil. This characteristic is measured under very preciseconditions, dictated by the standard ASTM D97B. It is generally assumedthat a compound belongs to the class of flow-point depressors if it iscapable of causing a decrease of the flow point by at least 6° C. for arate of utilization not exceeding 0.2% by weight of the polymericadditive.

The following nonlimiting examples show the advantages brought about bythe invention for different crudes.

EXAMPLE XVIII Modification of the Flow Point of a Crude from Gabon

The oil tested is a crude oil with a density of 852 kg/m³ (15° C.) andwith a paraffin content (determined by gas chromatography) of 15%. Itsflow point, measured under the conditions of the standard ASTM D 97 B,is 18° C.

In Table II, which follows, the flow points obtained for twocompositions with 37% additive described in Examples I to XVII above andthe differences in flow points observed in comparison to the untreatedcrude are reported.

It is noted that the optimum efficacy obtained with copolymer VII(70/30) is considerably improved with the terpolymer XV, which could beconsidered overall as a copolymer of 4-vinylpyridine and the copolymerVII in the weight ratio of 5/95 (or more precisely, 5/66.5/28.5), to thepoint that the lowering of the flow point can no longer be measured withthe tests adopted commonly (flow point lower than −45° C.).

TABLE II composition at 37% flow point (° C.) ΔT (° C.) example 100 ppm200 ppm 100 ppm 200 ppm I +6 −3 −12 −21 Ia 0 −3 −18 −24 II 0 −6 −18 −24III 0 −9 −18 −27 IV −6 −9 −24 −27 Shell Swimm 5X^(a)) −6 −9 −24 −27 V−12 −15 −30 −33 VI −15 −18 −33 −36 VII −18 −21 −36 −39 VIII −3 −6 −21−24 IX +6 +3 −12 −15 X −15 −15 −33 −33 XI −12 −12 −30 −30 XII +3 +3 −15−15 XIII −15 −15 −33 −33 XIV −9 −12 −27 −30 Shell Swimm 11T^(b)) −6 −12−24 −30 XV ≦27 ≦27 −45 −45 minimum minimum III + IX (70/30) −6 −15 −24−33 ^(a))Shell Swimm 5X is a composition with 50% by weight of a C₁₈-C₂₂“non-U”alcohol acrylate homopolymer sold by Shell. ^(b))Shell Swimm 11Tis a composition with 50% by weight of a C₁₈-C₂₂ “non-U”alcohol acrylatecopolymer and vinylpyridine sold by Shell.

The graph in FIG. 2 shows the lowering of the flow point of this Gaboncrude with 100 ppm of a composition with 37% “non-U” 18-22 acrylatecopolymer/“U” alcohol acrylate centered at C₃₀, as a function of thepercentage of acrylate C₃₀ in the copolymer. This graph shows clearlythe interest of copolymers carrying 5 to 50% “U” alcohol acrylatecentered at C₃₀ on this type of crude oil, and more particularly, thatof the copolymer of Example VII with 30% “U” alcohol acrylate centeredat C₃₀ as well as the 50% threshold, below which one observes asignificant lowering of the efficacy in combination with the lowersolubility of the copolymer. This efficacy cannot be found at such ahigh level with the 70/30 mixture by weight, corresponding to “non-U”C₁₈₋₂₂ and “U” C₃₀ homopolymers, respectively, for the same reasons.

The graph reproduced on FIG. 3 is the curve of the gain of the flowpoint of this same crude from Gabon as a function of the addition ofvarious quantities of the products of Examples IV and VII (compositionswith 37%). It permits evaluation of the improvement obtained withComposition Example VII of the invention with this crude oil, comparingit to one of the actual reference products present on the market, suchas Shell Swimm 5X®. A supplementary gain of efficacy is obtained withthe aid of the addition of 4-vinylpyridine according to Example XV.

EXAMPLE XIX Modification of the Flow Point of an Egyptian I Crude

The oil tested is a crude with a density of 845 kg/m³ (15° C.) and aparaffin content of 15%. Its flow point, measured under the conditionsof standard ASTM D97B, is +15° C.

Table III shows the flow points obtained with different compositions and37% additive, for two contents, described in the preceding example aswell as the deviations of the flow point in comparison to the untreatedcrude.

TABLE III composition with 37% flow point (° C.) ΔT (° C.) example 1000ppm 1500 ppm 1000 ppm 1500 ppm I +6 +3 −9 −12 IV −3 −6 −18 −21 ShellSwimm 5X −3 −6 −18 −21 VII −6 −9 −21 −24 III + IX (70/30) −3 −6 −18 −21

The same remarks as, for example XVIII, can be made for this crude oil,which is more difficult to treat, the useful doses thus being between1000 and 1500 ppm.

EXAMPLE XX Modification of the Flow Point of an Egyptian II Crude

The oil tested is a crude with a density of 820 kg/m³ (15° C.) and aparaffin content of 20-25%. Its flow point is 27°-30° C.

Table IV shows the flow points obtained with different compositionshaving 37% additive, for two contents, described in the precedingexample as well as the flow temperature deviations in comparison to theuntreated crude.

TABLE IV composition at 37% flow point (° C.) ΔT (° C.) example 1000 ppm1500 ppm 1000 ppm 1500 ppm I +21 +18 −9 −12 IV +15 +12 −15 −18 ShellSwimm 5X +12 +12 −18 −18 VII +9 +6 −21 −24 III + IX (70/30) +18 +8 −12−21

The same remarks as were made for Example XIX on this example of crudeoil having a flow point of 30° C., the useful doses are, here too,between 1000 and 1500 ppm.

The curves of FIGS. 4 and 5 illustrate on the one hand the improvementof the thermal susceptibility with regard to viscosity of a crude oil bythe addition of 1000 ppm of composition VII (with 37% polymer), thebenefit of which is a significant lowering of its viscosity at lowtemperatures and, on the other hand, a beneficial influence on the flowthreshold (yield value) at 15° C.

EXAMPLE XXI Modification of the Flow Point of an Egyptian III Crude

The oil tested is a crude having a density of 843 kg/m³ (15° C.), theparaffin content of which is 10.4%. Its flow point is +9° C.

Table VI shows the flow points obtained with 30 ppm of variouscompositions with 37% additive as well as the deviations of the flowtemperature in comparison to the untreated crude.

TABLE VI composition with 37% flow point (° C.) ΔT (° C.) example 30 ppm30 ppm IV  0 −9 Shell Swimm 5X −24 −33 VII −27 −36 Shell Swimm 11T −12−21 XV ≦24 ≦33

Here, too, one notes the remarkable effectiveness of additive VII andthat of the terpolymer XV.

EXAMPLE XXII Modification of the Flow Point of a Syrian Crude

The oil tested is a crude with a density of 870 kg/m³ (15° C.), theparaffin content of which is 6%. Its flow point is 18° C.

Table V reports the flow points obtained with different compositions at37% additive, described in the preceding example, for two contents aswell as the changes of the flow point in comparison to that of theuntreated crude.

TABLE V composition at 37% flow point (° C.) ΔT (° C.) example 100 ppm200 ppm 100 ppm 200 ppm I −3 −9 −21 −27 IV −9 −12 −27 −30 Shell Swimm 5X−6 −9 −24 −27 VII −15 −21 −33 −39 III + IX (70/30) −6 −12 −24 −30

This novel example had no other goal but to confirm the broad spectrumof activity of the additives according to the invention and theirsuperiority in comparison to the products present on the market.

All these examples demonstrate the remarkable and unexpected efficacy ofcopolymers of acrylates of primary fatty alcohols with a “U”distribution and of the compositions containing them according to theinvention, with regard to the global improvement of the behavior of thecrude oils, notably with a large lowering of the flow point and of thethreshold of flow of crude oils containing the additives.

What is claimed is:
 1. Copolymers of alkyl acrylates or ofalkyl/vinylpyridine acrylates with a weight-average molecular weightM_(w) between 5000 and 500,000, in which the monomeric acrylate unitsthat participate in the polymer chain are the following units

in which R is H or CH₃, and in which Ri are saturated linear aliphaticalcohol Ri-OH group residues where i represents the number of carbons ofthese groups which extend between 10 and 50 carbon atoms and which havethe characteristic of following a distribution law which is thesuperposition of a “U” distribution law in which the i values are evennumbers ranging in the upper part of the interval 24-50, the centeredvalue of which is i_(u), and the “non-U” distribution law in which the Ivalues are even or odd numbers ranging in the low 10-22 part of theinterval, and the centered value i_(nu) of which i_(nu)<i_(u), theweight ratio of all the units

distributed according to the “U” law to all the units distributedaccording to the “non-U” law ranging from 1:99 to 50:50.
 2. Copolymeraccording to claim 1, wherein the “non-U” units are units of acrylatesof alcohols with about 10-22 carbon atoms and the “U” units are units ofacrylates of alcohols with about 24-50 carbon atoms.
 3. Alkyl acrylatecopolymers according to claim 1, wherein the copolymers carry, besidesthe acrylate units, 1 to 10% vinylpyridine units, counted by weight withrespect to that of the copolymer.
 4. Method for obtaining copolymersdescribed according to claim 1, wherein the polymerization of a mixtureof monomers in which a part of the monomeric acrylic or methacrylicesters

obeys a “U” distribution law and the complementary part of the estermonomers obeys a “non-U” distribution law, the weight ratio of all theesters distributed according to the “U” law and all the estersdistributed according to the “non-U” law ranging from about 5:95 toabout 50:50.
 5. Method according to claim 4, wherein the mixture ofacrylic or methacrylic esters is obtained by mixing esters of each ofthe “U” and “non-U” categories of distribution in a weight ratio of 1:99to 50:50.
 6. Method according to claim 4, in which the mixture of theacrylic or methacrylic esters is obtained by prior mixing of alcohols ofeach of the “U” and “non-U” distribution categories, followed by theiresterification with acrylic or methacrylic acid.
 7. Method according toclaim 4, wherein the operation is carried out in a solvent in which themonomers as well as the copolymer are soluble and the boiling point ofwhich is less than 300° C.
 8. Method according to claim 7, wherein thesolvent is xylene.
 9. Additive intended to lower the flow point ofpetroleum crude oils and to improve their rheological behavior, whereinit consists of copolymers described according to claim 1 and of anaromatic and/or aliphatic solvent, the weight ratio of the copolymer inthe additive being between 2 and 90%.
 10. Composition comprising apetroleum crude oil and a copolymer as described in claim 1, wherein thecontent of copolymers is between 5 and 5000 ppm.
 11. Copolymer accordingto claim 1, wherein the M_(w) is between 40,000 and 350,000, the weightratio is between 5:95 to 50:50.
 12. Method according to claim 5, whereinthe weight ratio is from 5:95 to 50:50.
 13. Additive according to claim9, wherein the weight ratio of the copolymer in the additive is between20 and 70%.
 14. Composition according to claim 10, wherein the contentof copolymers is between 10 and 2000 ppm.